Converting chromates into bichromates.



UNITED STATES PATENT OFFICE.

CHEMISOHE FABRIK GRIESHEIM ELECTRON, .OF FRANKFORT-ON-THE- MAIN,GERMANY.

CONVERTING CHROMATE S INTO BICHROIVIATES.

Specification of Letters Patent.

Patented Dec. 18, 1906.

. Application filed July 9,1903. Serial No; 164.901- v To all] 1072 07717115 may concern:

Be it known that I, ROBERT SUoiIY, a subect of the Emperor ofAustria-Hungary, residing and having my POSt-Ol'l'lCG address at 1Jahnstrasse, Griesheimon-the\iain, Gerwhen a neutral solution ofchromate is subjected in ltoth compartments of an, electrolytic cell tothe action of electricity, the coinpartments being separated from eachother by a diaphragm and the anode being of a material not attacked bythe solution, While the cathode is of a material which does not reducethe alkali chromate. Bicbroinate and oxygen are formed in theanode-compartment in accordance with the following equation:

K-zOrOi CF04 I lzOT'i 07 while the action taking place in thecathodecompartment results in the formation of caustic alkali andhydrogen in accordance with the following equation:

The yield is from eighty to ninety per cent. of the theoretical when theamount of alkali contained in the cathode solution is not too high.Haussermann has already proposed to convert by electrolysis neutralchromate into bichromate by placing the chromate in theanode-compartment and charging the cathode-compartment with water, (DingZeus Polytechnisches J carnal, 288, 161.) This process has thedisadvantage of requiring at the beginning of the electrolytic processan electric current of very high voltage on account of the resistanceoffered to the current by the cathode liquid, and the yield in alkaliand bichromate is very poor on account of the passageof OH ions into theanode-compartment. If, however, in accordance with this invention achromate solution be introduced into the cathode-compartment, a goodyield can be obtained with an electric current of low voltage, becausethe transference of the negative electricity to the anode is effectedsolely by the CrO ions.

The following examples will show how this invention can be carried outin practice:

In an iron trough connected to the negative pole of a source ofelectricity is placed a cell made of a material capable of acting like adiaphragm and dividing the trough into two compartments.

Into both the outer (the cathode) compartment and the inner (the anode)compartment a saturated solution of chromate is introduced, and theanode-compartment is provided with an insoluble anodesuch as lead orplatinumfor example. The current is then passed through the electrolyticapparatus until the chromate is converted into bichromate. The capacityof the cathodecompartment should be such that the amount of alkali isabout one hundred grams per liter after the conversion of the chromateinto bichromate is completed. It is also possible to work independentlyof the duration of the action going on at the anode by causing acirculation of the solutions in the cathodecompartment: To keep thevoltage low, it is advisable to heat the bath to a temperature of fromto centigrade.

A saturated or concentrated chromate solution is used to give to thecathode liquid a good conducting quality and to make the yield of thecaustic alkali and of bichromate so great as to practically attain thetheoretical one. The transference of the negative electricity to theanode is eifected at the beginning of the electrolysis only by the CrOions, and only at or near the end of the process when the alkali hasbeen generated by electrolysis do the OH ions also participate in theconduction of electricity. Only the OrO ions go through. the diaphragminto the anode-space, so that in the anode-space only OrO and Or O ionsare present, and as there is no other kind of ions added the yield canonly be reduced at the end of the process when in the cathode-space theconcentration of the OH ions has become so strong that said ionsparticipate in the conduction of the current and enter into theanode-space.

When the alkaline contents of the cathode solution are suflicientlyhigh, the said solution can be concentrated by evaporation, the chromatestill-present in the solution being i thereby precipitatedquantitatively while hasbeen wholly transformed into b'i'chromate setforth of converting chromate into ibichrothe alkali. lye that remainshas a strength of 50 Baum.

The anode solution can after thechromate be discharged directly into thecrystallizing vessel.

Having now particularly described and ascertained the nature of thisinvention and in what manner the same is to be performed, I declare thatwhat I claim is The method substantially as hereinbefore mate and thesimultaneous production of an alkali which consists in introducing a's'aturated neutral solution of alkali chromate into i the anode xandcathodecompartments of an electrolytic cell separatedfrom each other bya diaphragm, employing as electrodes an anode not attacked by thesolution and a cathode which will not reduce the chromate,

I and electrolyzing the solution whereby at the beginning thetransference of the negative electricity to the anode iseffected solelyby the CrO ions and caustic alkali is obtained inthe cathode-compartmentand a pure solution of bichromate is obtained in the anodecompartment.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

g ROBERT SUCHY. V Vitnesses FRANZ HAss AonER,

MICHAEL POLK.

